A percussion fuse for artillery training ammunition such as mortar and howitzer projectiles. The training fuse assembly includes a body adapted for connection to a projectile body, a composition signal charge mountable within the fuse body and emitting report, smoke, and flash signals, and a striker unit for detonating the signal charge upon impact with a desired target. A combination safety system prevents premature detonation of the charge during handling, transportation, loading, and initial in-flight upward travel of the projectile. The fuse only becomes fully armed when the projectile reaches its terminal velocity and begins its downward flight toward the designated target. The armed fuse is highly sensitive and even upon impact with water will detonate in super quick fashion to discharge the entire signal before the projectile disappears below the surface of the water.